The present invention relates to an optical article and, more particularly, to an optical article having at least one optical fiber and having a printable layer with an indicia printed thereon.
Conventional fiber optic cables comprise optical fibers that conduct light which is used to transmit voice, video, and data information. An optical ribbon includes a group of optical fibers that are coated with a printable ribbon common layer, which common layer may be of the ultraviolet (UV) light curable type. Typically, such a ribbon common layer is extruded about a group of optical fibers that have been arranged in a planar array, and is then irradiated with a UV light source that cures the ribbon common layer. The cured ribbon common layer protects the optical fibers and generally aligns the respective positions of optical fibers in the planar array.
To further illustrate the background of the present invention, FIGS. 2-5 show known optical ribbons. More specifically, FIG. 2 shows adjacent optical ribbons 14-1 and 14-2 of a known ribbon stack 12. Optical ribbons 14-1,14-2 each include optical fibers 15 encased in a ribbon common layer 19. A craftsman may gain access to optical ribbons 14-1,14-2 by cutting away outer portions of the cable to expose ribbon stack 12. Once stack 12 is exposed, the craftsman may desire to distinguish between and classify the ribbons according to, for example, which telecommunications circuit they are to be associated with. To classify the ribbons, the craftsman may look for indicias on each ribbon, for example, a series of alpha-numeric characters that define a label or indicia 16 (FIG. 3).
As shown in FIG. 3, indicia 16 includes a series of printed dots 17 that collectively depict the alpha-numeric characters. Dots 17 are small masses of ink material that present bump-like (FIGS. 4-5) and/or trough-like (not shown) irregularities on and/or in the surface of common layer 19. The characters of indicia 16 are made at a conventional print pitch P of about 4.21 to 5.5 characters per centimeter (ch/cm). Indicias 16 are typically repeated longitudinally on the ribbon at print spacing intervals. A typical print spacing is about 150-200 mm and above. A 5.5 ch/cm print pitch on ribbon 14-1 as shown in the transverse cross section of FIG. 4, and the longitudinal cross section of FIG. 5, results in dots 17a of indicia 16 very nearly touching, and dots 17b being overlapped to some extent. Rather than being discrete dots, dots 17a, 17b may in some places form lines. Moreover, dots 17 present, at regular intervals, the bump-like and/or trough-like irregularities on and/or in the surface of common layer 19 at regular transverse spacings St (FIG. 4) and longitudinal spacings S1 (FIG. 5). Spacings St and S1 are constant and non-randomized. A printing machine causes the dots to be transversely and longitudinally made at the regular intervals in and/or on the ribbon common layer directly over or adjacent to the optical fibers.
Known ribbon indicia of the printed ink type may be printed on the ribbon common layer or on optical fibers. U.S. Pat. No. 5,485,539 discloses printed ink dots on a ribbon common layer that define layered dots that form symbols. A transparent, anti-abrasion coating may be applied over the printed ink dots.
U.S. Pat. No. 5,119,464 discloses a process for directly marking optical fibers with ink as they move in a planar array before being coated with a protective envelope. An ink jet sprays the optical fibers with ink as the fibers move along a production line. The ink jet is driven to reciprocate in a direction that is transverse to the direction of movement of the fibers along the production line. As this occurs, bands of ink are deposited on the optical fibers. The bands of ink are staggered with respect to each other across the array of optical fibers. The result is a group of optical fibers each having a characteristic ink band spacing.
The foregoing disclosures do not teach or suggest a cognizance of any relationship between the printed indicia and attenuation loss in the optical fibers. On the other hand, the present inventors have discovered that printing dots on an optical ribbon at regular intervals can contribute to an undesirable delta attenuation. Attenuation indicates a degradation in performance due to a loss in power from one point to another along a light waveguide path, e.g., an optical fiber. Attenuation is generally measured in terms of decibels per kilometer (dB/km) at a specified wavelength. Attenuation varies with the wavelength of light propagating through the optical fiber. A delta attenuation is the change in attenuation that a modified optical fiber experiences as measured relative to a reference attenuation measurement of the optical fiber in a pre-modified state. For example, delta attenuation is a measure of the increase in attenuation a colored optical fiber experiences as compared to the attenuation the optical fiber experienced without the coloring layer. Since increases in attenuation degrade the performance of an optical fiber, high delta attenuations are undesirable. Attenuation may be caused by microbending or macrobending of the optical fiber. A microbend loss may result from the optical fiber passing over small bumps. Optical fibers have windows of low-loss wavelength regions where the fiber will carry light with little attenuation. One of the windows is known as a 1310 nm wavelength region, and another is in the 1550 nm wavelength region.
FIG. 6 is a graph showing attenuation, as a function of wavelength, in optical fibers of an optical ribbon having a known indicia with dot spacings St,SI made at regular, non-randomized intervals. The inventors of the present invention have discovered a relationship between spacing of ink shapes and attenuation, for example, to the effect that the known indicia creates undesirable attenuation or spectral bumps in the 1310 nm wavelength region. Even for a range of mode field diameters (MFD), e.g., 9.08, 9.18, and 9.31, the attenuation bumps still exist, apparently due to a harmonic response caused by the regularity of the spacing on the optical fibers.
One aspect of the present invention is a method of printing ink shapes on an optical article so that optical attenuation is controlled. The optical article may include at least one optical fiber and a printable layer associated with the optical fiber. The method comprises the steps of moving the optical article along a manufacturing line, supplying a randomized pulse input to a printing apparatus, and printing randomly spaced ink shapes on the optical article.
Another aspect of the present invention is an optical article and a printable layer associated with the optical article, the printable layer including at least one indicia thereon. The indicia includes randomly spaced printed ink shapes for controlling optical attenuation.
Another aspect of the present invention is a printing apparatus and randomizing system for printing randomized ink shapes on an optical article. The randomizing system comprises a noise generator generating a random pulse and a uniform pulse source generating a uniform pulse the uniform and random pulses being summed to define a randomized variable pulse. The printing apparatus is operatively associated with the randomizing system, and includes printer controls that receive the randomized variable pulse from the randomizing system as an input. The printing apparatus comprises an ink jet stream directed toward the optical article whereby the optical article is printed with randomly spaced ink shapes.